CA1184783A - Bridge excitation for sensor used on a vortex shedding flow meter - Google Patents
Bridge excitation for sensor used on a vortex shedding flow meterInfo
- Publication number
- CA1184783A CA1184783A CA000417484A CA417484A CA1184783A CA 1184783 A CA1184783 A CA 1184783A CA 000417484 A CA000417484 A CA 000417484A CA 417484 A CA417484 A CA 417484A CA 1184783 A CA1184783 A CA 1184783A
- Authority
- CA
- Canada
- Prior art keywords
- sensor
- coil
- circuit
- vortex shedding
- burst
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
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Abstract
ABSTRACT OF THE DISCLOSURE
A sensor circuit and method of operating a vortex shedding flow meter is disclosed which utilized A.C. single cycle bursts to intermittently drive a sensor which changes its state with the vortex shedding frequency.
The bursts are spaced in time by an amount larg er than the burst duration.
A sensor circuit and method of operating a vortex shedding flow meter is disclosed which utilized A.C. single cycle bursts to intermittently drive a sensor which changes its state with the vortex shedding frequency.
The bursts are spaced in time by an amount larg er than the burst duration.
Description
BRIDGE EXCITATION FOR SENSOR USED ON A
VORTEX SHEDDING FLOW METER Case 4437 ~ . _ - Fleld and Ba~ round of the Invention The present invention relates in general to circuitry for vortex shedding flow meters and, ln parti-cular, to a new and useful circu;t and method of driving the sensor connected to a vort~x shedding flow meter to reduce energy consumption and heating.
Vortex shedding flow meters are utllized ~o lQ measure the volumetric flow of fluids by presenting a non-streamlined obstruction termed a bluff body in the flow path. As the flowing fluid separates around the obstruction, vortices are produced in the wake of the obstruction wh~ch alternate from one side of the obstruction to the other. The number of these vortices per unit time is directly proportional to the vol~netric flow rate. The numher of vortices thus can be counted to provide a measure of the flow rate.
It is known to utilize a bridge circuit to sense the passing of these vortlces which has one resistor or other element which changes with the passage of each vortex. Circuit elements are connected to the bridge to count the thus sensed passage of vortices and provide a signal which ls proportional to the flow rate of the fluid to be measured.
Transformers are utili~ed to drive one side of the bridge and also to ~ap ~he signal from the other side of the bridge. When large drivlng voltages are utilized, the sensor bridge has a tendency to heat and lose accuracy due t~ drlft ~nd also impairs useful life. Moreover, many transmitter applications do not have this high power available on a continuous basis.
SUMMARY QF THE INVENTION
The present invention is drawn to an lmproved method and circuitry for driving and sensing the signal from a sensing bridge utilized in a vortex sheddlng flow me~er.
Rather than continuously driving the bridge, it has been found advantageous to utilize an A.C. signal to drive the bridge sensor in discrete singly cycle bursts which are widely spaced. The sensor is thus activaged to sense the passing of vortices only during discrete time intervals, pro~iding a low average power to the sensor so that it remains in a stable state having increased product life.
Accordingly, an object of the present invention is to provide a method of operating a vortex sheddi.ng flow meter sensor circuit having a drivable sensor member wlth an output which varies at a vortex shedding frequency com-prising, driving the sensor member only during A.C. one cyclebursts, said bursts spaced in time by an amount larger than a duration of each burst.
Since the sensor is driven a~ a hlgh peak power, the sensltivity is improved~ as 1~ is direc~ly related to the peak drivlng power. This achieves a main object of the invention.
Another object of the invention is to provide a vortex shedding flow me~er clrcui~ comprising, a sensor which varies its state with a vortex shedding frequency, a drive circuit con~ected to said sensor having means for applylng A.C. single cycle bursts spaced in time by an amount greater than the duration of each burst, to the sensor, and a sensor circuit connected to said sensor for producing a signal corresponding to the vortex shedding frequency.
Another ob~ect is to provide isola~ion between the sensor and the output circuit to prevent grounding interactions.
Another object of the invention is to provide a sensor circuit for a vortex shedding flow meter which is simple in design, rugged in constructlon and economical to manufacture.
The various features of novelty which character-i~e the lnvention are pointed out with particulartly in the claims annexecl to and forming a part of this disclosure.
For a better understanding of the invention, its operating advantages and specific obJects attained by its uses, reference is made to the accompanylng drawings and descriptive matter in which a preferred embodimen~ of the invention is illustrated.
BRIEF DESCRIPTION OF THE DRAWINGS
In the Drawings:
Fig. 1 is a sche~atic represen~ation of a clrcuit utilized ~n accordance with the inventlon;
Fig. 2 shows a typlcal wave form which is applied to the bridge in the circui~ o Flg. 1, Fig. 3 shows the driving wave form applied ~o input 24 of the Fig. 1 circuit; and Fig. 4 shows the drlvln~ wave form applied to input 26 of the F~g. 1 circult.
DESCRIPTION OF THE PREFERRED EMODIMENT
Referring to the drawings 3 Fig. 1 shows a typical circu;t which can be utilized to practice the invention. A brldge generally designated 10 comprises four resistors Rl through R4. The bridge ls utilized as ~ strain gauge for sensing the passage of vort~ce6 past a bluff of a vortex shedding flow meter.
One of the resistors Rl acts as an active component of the bridge and reacts ~ the passage of a vortex ~0 by changing resistance. Another resistor, for example R~
acts as a dummy resistor and coopera~es with the two balancing resistors R2 and R3 in known fashion.
A bridge drive transformer Tl has one winding 12 connected across the north and south terminals 14 and 16 respectively of bridge 10. The other coil 20 of drive transformer Tl i.s connected to the collectors of two transistors Ql and Q2. The emitters of transistors Ql and Q2 are connected to a circuit common point 22. The bases of transistors Ql and Q~ are excited by ~irst and second dri~e signals applied to terminals 24 and 26 respectively, as shown in Figures 3 and 4; respectively.
~ 3 These drlv~ signals are rela~ed ~o the upper and lower half cycles of the Fig. 2 waveorm.
The eas~ and west terminal~ oE bridge 10 are connec~ed across one coil 28 of an lsolating signal S transformer T2. A ~ignal received from the br~dge 10 is supplied by the other coil 30 of transformer Tl ts a sample and hold circuit 3~. The sample and hold circuit 32 comprise flrst and second swit~hes Sl and S2 connected to two inpu~ of a differential am~lifler 34. Switches Sl j and S2 operate in conjunction wlth capacitors Cl and C2 to provide full-wave rectification of ~he output sig~al from transf~rmer T2. The dl~ferential ampli.fier provides a ~irct~t-common reference s-lgnal and has an output which shows the difference between the signals on capacitor Cl and capacitor C2. The wavP form at the o~tput of amplifier - 34 is then a sampled representation of the vortex frequency, with samples taken at intervals determined by the Flg. 2 peaks.
Figs. 3 and 4 show the wave for~ of A.C.
signals which are applied to terminals 24 and 26 to drlve transistors Ql and Q2. The A.C. signals deslgnated 40 and 42 comprise greatly spaced single cycle bursts 44 and 46.
A typical duty cycle of ten percent ls thus provided to the bridge drive vol~age applied to terminals 24, 26. The frequency of the bridge drive is selected to be at least five and preferably ten times that of the maximum vortex shedding frequency to be measured. The sensor in the form of bridge 10 is thus gated ON in single cycle and widely spaced bursts. This permits an increased drive level of approximately ten to one while permitting operation at low total power modes as dicated by a known 4-20 mA two-wire transmitter application.
i The invention also permits typical~ ten times hlgher bridge drives wi~hout introducing any additional heating problem ~Yer that which would be the case utilizing lower but con~nuous drive levels.
Sensitivity increases of typically ten times are ~hus gained by the low-duty cycle swi~ching technique.
In addition, a double incrPase is obtained for the full wave action of the sample and hold circuitry, and the signal path transormer contributes typically to a ~ive old increase in signal voltage.
While a specific embodiment of the invention has been shown and described in detail to illustrate the applicati.on of the prino~ples of the invention~ it will be understood that the invention may be embodied otherwisP
wi~hout departing from such principles.
VORTEX SHEDDING FLOW METER Case 4437 ~ . _ - Fleld and Ba~ round of the Invention The present invention relates in general to circuitry for vortex shedding flow meters and, ln parti-cular, to a new and useful circu;t and method of driving the sensor connected to a vort~x shedding flow meter to reduce energy consumption and heating.
Vortex shedding flow meters are utllized ~o lQ measure the volumetric flow of fluids by presenting a non-streamlined obstruction termed a bluff body in the flow path. As the flowing fluid separates around the obstruction, vortices are produced in the wake of the obstruction wh~ch alternate from one side of the obstruction to the other. The number of these vortices per unit time is directly proportional to the vol~netric flow rate. The numher of vortices thus can be counted to provide a measure of the flow rate.
It is known to utilize a bridge circuit to sense the passing of these vortlces which has one resistor or other element which changes with the passage of each vortex. Circuit elements are connected to the bridge to count the thus sensed passage of vortices and provide a signal which ls proportional to the flow rate of the fluid to be measured.
Transformers are utili~ed to drive one side of the bridge and also to ~ap ~he signal from the other side of the bridge. When large drivlng voltages are utilized, the sensor bridge has a tendency to heat and lose accuracy due t~ drlft ~nd also impairs useful life. Moreover, many transmitter applications do not have this high power available on a continuous basis.
SUMMARY QF THE INVENTION
The present invention is drawn to an lmproved method and circuitry for driving and sensing the signal from a sensing bridge utilized in a vortex sheddlng flow me~er.
Rather than continuously driving the bridge, it has been found advantageous to utilize an A.C. signal to drive the bridge sensor in discrete singly cycle bursts which are widely spaced. The sensor is thus activaged to sense the passing of vortices only during discrete time intervals, pro~iding a low average power to the sensor so that it remains in a stable state having increased product life.
Accordingly, an object of the present invention is to provide a method of operating a vortex sheddi.ng flow meter sensor circuit having a drivable sensor member wlth an output which varies at a vortex shedding frequency com-prising, driving the sensor member only during A.C. one cyclebursts, said bursts spaced in time by an amount larger than a duration of each burst.
Since the sensor is driven a~ a hlgh peak power, the sensltivity is improved~ as 1~ is direc~ly related to the peak drivlng power. This achieves a main object of the invention.
Another object of the invention is to provide a vortex shedding flow me~er clrcui~ comprising, a sensor which varies its state with a vortex shedding frequency, a drive circuit con~ected to said sensor having means for applylng A.C. single cycle bursts spaced in time by an amount greater than the duration of each burst, to the sensor, and a sensor circuit connected to said sensor for producing a signal corresponding to the vortex shedding frequency.
Another ob~ect is to provide isola~ion between the sensor and the output circuit to prevent grounding interactions.
Another object of the invention is to provide a sensor circuit for a vortex shedding flow meter which is simple in design, rugged in constructlon and economical to manufacture.
The various features of novelty which character-i~e the lnvention are pointed out with particulartly in the claims annexecl to and forming a part of this disclosure.
For a better understanding of the invention, its operating advantages and specific obJects attained by its uses, reference is made to the accompanylng drawings and descriptive matter in which a preferred embodimen~ of the invention is illustrated.
BRIEF DESCRIPTION OF THE DRAWINGS
In the Drawings:
Fig. 1 is a sche~atic represen~ation of a clrcuit utilized ~n accordance with the inventlon;
Fig. 2 shows a typlcal wave form which is applied to the bridge in the circui~ o Flg. 1, Fig. 3 shows the driving wave form applied ~o input 24 of the Fig. 1 circuit; and Fig. 4 shows the drlvln~ wave form applied to input 26 of the F~g. 1 circult.
DESCRIPTION OF THE PREFERRED EMODIMENT
Referring to the drawings 3 Fig. 1 shows a typical circu;t which can be utilized to practice the invention. A brldge generally designated 10 comprises four resistors Rl through R4. The bridge ls utilized as ~ strain gauge for sensing the passage of vort~ce6 past a bluff of a vortex shedding flow meter.
One of the resistors Rl acts as an active component of the bridge and reacts ~ the passage of a vortex ~0 by changing resistance. Another resistor, for example R~
acts as a dummy resistor and coopera~es with the two balancing resistors R2 and R3 in known fashion.
A bridge drive transformer Tl has one winding 12 connected across the north and south terminals 14 and 16 respectively of bridge 10. The other coil 20 of drive transformer Tl i.s connected to the collectors of two transistors Ql and Q2. The emitters of transistors Ql and Q2 are connected to a circuit common point 22. The bases of transistors Ql and Q~ are excited by ~irst and second dri~e signals applied to terminals 24 and 26 respectively, as shown in Figures 3 and 4; respectively.
~ 3 These drlv~ signals are rela~ed ~o the upper and lower half cycles of the Fig. 2 waveorm.
The eas~ and west terminal~ oE bridge 10 are connec~ed across one coil 28 of an lsolating signal S transformer T2. A ~ignal received from the br~dge 10 is supplied by the other coil 30 of transformer Tl ts a sample and hold circuit 3~. The sample and hold circuit 32 comprise flrst and second swit~hes Sl and S2 connected to two inpu~ of a differential am~lifler 34. Switches Sl j and S2 operate in conjunction wlth capacitors Cl and C2 to provide full-wave rectification of ~he output sig~al from transf~rmer T2. The dl~ferential ampli.fier provides a ~irct~t-common reference s-lgnal and has an output which shows the difference between the signals on capacitor Cl and capacitor C2. The wavP form at the o~tput of amplifier - 34 is then a sampled representation of the vortex frequency, with samples taken at intervals determined by the Flg. 2 peaks.
Figs. 3 and 4 show the wave for~ of A.C.
signals which are applied to terminals 24 and 26 to drlve transistors Ql and Q2. The A.C. signals deslgnated 40 and 42 comprise greatly spaced single cycle bursts 44 and 46.
A typical duty cycle of ten percent ls thus provided to the bridge drive vol~age applied to terminals 24, 26. The frequency of the bridge drive is selected to be at least five and preferably ten times that of the maximum vortex shedding frequency to be measured. The sensor in the form of bridge 10 is thus gated ON in single cycle and widely spaced bursts. This permits an increased drive level of approximately ten to one while permitting operation at low total power modes as dicated by a known 4-20 mA two-wire transmitter application.
i The invention also permits typical~ ten times hlgher bridge drives wi~hout introducing any additional heating problem ~Yer that which would be the case utilizing lower but con~nuous drive levels.
Sensitivity increases of typically ten times are ~hus gained by the low-duty cycle swi~ching technique.
In addition, a double incrPase is obtained for the full wave action of the sample and hold circuitry, and the signal path transormer contributes typically to a ~ive old increase in signal voltage.
While a specific embodiment of the invention has been shown and described in detail to illustrate the applicati.on of the prino~ples of the invention~ it will be understood that the invention may be embodied otherwisP
wi~hout departing from such principles.
Claims (8)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A method of operating a vortex shedding sensor circuit having a drivable sensor member which produces an output that varies at a vortex shedding frequency comprising:
driving the sensor member only during single cycle A. C . bursts which are spaced in time by an amount greater than a duration of each burst.
driving the sensor member only during single cycle A. C . bursts which are spaced in time by an amount greater than a duration of each burst.
2. A method according to claim 1, wherein said A.C. bursts are chosen to have a duty cycle of ten percent.
3. A method according to claim 1, wherein the sensor circuit includes a drive transformer having a drive coil, the method further comprising applying a positive half cycle of each burst determined by driving one end of the coil and a negative half cycle of each burst determined by driving the opposite end of the coil.
4. A method according to claim 1, wherein a frequency of said A.C. single cycle bursts is chosen to be at least five times a maximum of the vortex shedding frequency.
5. A vortex shedding flow meter circuit comprising:
a sensor which varies its state with a vortex shedding frequency;
a drive circuit connected to an input of said sensor having means for applying A.C. single cycle bursts spaced by an amount greater than the duration of each burst to said sensor for driving said sensor to change its state with the vortex shedding frequency; and an output circuit connected to an output of said sensor for producing a signal corresponding to a rate at which said sensor varies its state.
a sensor which varies its state with a vortex shedding frequency;
a drive circuit connected to an input of said sensor having means for applying A.C. single cycle bursts spaced by an amount greater than the duration of each burst to said sensor for driving said sensor to change its state with the vortex shedding frequency; and an output circuit connected to an output of said sensor for producing a signal corresponding to a rate at which said sensor varies its state.
6. A circuit according to claim 5, wherein said sensor comprises a bridge having at least one element which changes its state with the vortex shedding frequency and balancing elements, said drive circuit comprising a bridge drive transformer having an output coil connected to said bridge and an input coil, said drive means effective to apply a positive one half cycle of each burst to one and of said input coil and a negative one half cycle of each burst to an opposite end of said coil.
7. A circuit according to claim 6, wherein said drive means comprises a first transistor connected to one end of said input coil and a second transistor connected to an opposite end of said input coil, each of said trans-istors having bases respectively connectable to determine positive and negative half cycles of each burst.
8. A circuit according to claim 7, wherein said output circuit comprises an isolating transformer having an input coil connected to said bridge and an output coil, a sample and hold circuit connected to said output coil and a differential amplifier connected to said sample and hold circuit.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US32963381A | 1981-12-11 | 1981-12-11 | |
| US329,633 | 1981-12-11 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1184783A true CA1184783A (en) | 1985-04-02 |
Family
ID=23286318
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000417484A Expired CA1184783A (en) | 1981-12-11 | 1982-12-10 | Bridge excitation for sensor used on a vortex shedding flow meter |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1184783A (en) |
-
1982
- 1982-12-10 CA CA000417484A patent/CA1184783A/en not_active Expired
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